To prevent water pollution in furtherance of the goals of the Clean Water Act, regulations and enforcement actions have historically focused on the output of wastewater treatment facilities. However, in recent years, the technology for treating wastewater has largely matured to the point that treatment facilities are decreasingly the source of significant water pollution. To further eliminate potential water pollution, the United States Environmental Protection Agency, municipalities, and sanitary sewer system authorities have recently refocused their attention and resources on the networks of pipes that transport wastewater to the treatment facility.
These piping networks may be constructed as a combined wastewater and storm water system, or be dedicated exclusively to the transport of wastewater. In either case, untreated wastewater can overflow from the system into the environment. For the health of the community and environment, and to remain in compliance with the law, a sanitary sewer system authority must prevent such overflows. To comply with a permit to operate a sanitary sewer system, a sewer authority must “take all reasonable steps to minimize or prevent any discharge . . . which has a reasonable likelihood of adversely affecting human health or the environment.” 40 CFR 122.41(d).
A sanitary system overflow (SSO), can be caused by a number of factors. The primary causes are restrictions and blockages in the sewer system, most often caused by the accumulation of debris, roots and/or grease in a sewer pipe. In wet weather conditions, storm water runoff may overwhelm the capacity of a combined sanitary sewer and storm water system, and cause the system to overflow.
In the past, municipalities and sanitary system authorities have addressed actual and potential sanitary sewer system overflows in a number of ways. Many authorities have simply built additional or redundant capacity into their piping systems to prevent overflows. Studies have shown, however, that restrictions and blockages are the primary causes of overflows, not a lack of capacity in the system. Thus, simply adding additional capacity leads to piping systems that are underutilized and more expensive than necessary to serve the sanitary needs of the community.
The infiltration and inflow of storm water into a dedicated sanitary sewer system is a significant concern. During wet weather conditions, storm water runoff may infiltrate a dedicated sanitary sewer system. Even if the infiltration does not lead to a system overflow, infiltration and inflow of storm water into a sanitary sewer system leads to increased costs because the storm water inflow must then be treated along with the untreated sewage.
Restrictions, infiltrations and inflows lead to increased costs and potential environmental problems, and an SSO may result in untreated sewage being released into the environment or backing up into residential basements. To avoid these problems, municipalities and sanitary sewer system authorities attempt to identify potential points of restriction, infiltration, and inflow in a sanitary sewer system and address any problems causing the infiltration and inflow.
Storm water runoff may infiltrate a dedicated sanitary sewer system through broken or ruptured pipes. However, because these pipes are typically underground, the infiltration point is difficult if not impossible to locate and detect by visual inspection during a wet weather event. Although the location of an overflow may be obvious, the source of the extra water that is actually causing the overflow may be a mystery. Also, in most cases, the only evidence of infiltration is the increased burden on treatment facilities during a wet weather event.
To detect and identify infiltration points, municipalities and sanitary sewer system authorities typically monitor the flow in the system during a wet weather event. Flow measurements may be taken at a multitude of points in the system. These flow measurements may then be compared with flow measurements during dry weather to determine if the wet weather has increased flow at a particular point or points in the system. Such flow measurement studies, however, are difficult and expensive to administer, in addition to being difficult to schedule due to the unpredictability of the weather.
Some larger authorities have employed complex and expensive evaluation methods to identify potential causes of sewer infiltration and SSO's. These methods often include the use of expensive devices for monitoring flow at different points in the system and the employment of personnel and/or consultants to collect and analyze data from the flow monitoring devices. The data is often analyzed by consultants using proprietary software by paid consultants.
Many devices for measuring and monitoring fluid flow velocity have been developed. The velocity of some fluid flows may be measured by placing a paddle wheel or turbine in the flow and measuring the rate of spin of the device. Fluid flow velocity may also be measured by placing a bending vane type sensor in the flow and measuring the deflection of the vane or by placing a restriction on the flow and measuring the differential pressure of the restricted flow. Although inexpensive compared to other measurement techniques, these types of devices necessarily obstruct the fluid flow. In addition, these types of devices are not well suited for certain applications because the measurement device cannot be easily inserted and secured in the fluid flow.
More advanced measurement devices that do not obstruct fluid flow include ultrasonic and magnetic flow meters. Although more precise and reliable, these types of devices are typically very expensive, limiting their application. Also, due to limitations of the technology, these devices are often not well suited for measuring irregular flows that may include solids. These types of flow meters are also disadvantageous for many applications because they are difficult to install, calibrate, and operate.
Another type of flow measurement device is based on the known principal that vortices are created on the downstream side of an object when fluid flows past the object. If the object is allowed to move, these vortices will cause the object to oscillate periodically in the fluid flow. An example of this common phenomenon is a flag flapping in the wind. To measure flow velocity using this principal, an object is inserted in a fluid flow and allowed to oscillate. As the velocity of flow increases, the frequency of oscillation increases in relation to the flow. By measuring the frequency of oscillations of the object in the fluid flow, the velocity of the fluid flow may be determined.
A flow meter that utilized this phenomenon is disclosed in U.S. Pat. No. 2,809,520 issued to Richard, where an elongated sensing element is placed in a fluid flow, causing the sensor to oscillate. The mechanical oscillations of the sensor are converted to an electrical signal using different types of transducers including a piezoelectric crystal, electrical contacts and a condenser plate. The frequency of the electrical signal can then be read on a frequency meter and used to determine the velocity of the fluid flow.
An accelerometer is another device for measuring oscillations. Accelerometers can also measure acceleration, detect and measure vibrations, or measure inclination. Accelerometers sometimes consist of little more than a suspended cantilever beam or mass with a deflection sensor. A range of accelerometers are available to detect a magnitude of accelerations. Single axis, dual axis, and three axis accelerometers are available. Accelerometers have been used to measure the vibration of cars, machines, buildings, and the earth itself. Accelerometers have been incorporated into media players and handheld gaming devices such as Apple's iPhone™ and Nintendo's Wii™ controller.
The vortices caused by an object in a fluid flow may also be detected and measured to determine flow velocity. A flow meter utilizing this technique is disclosed in U.S. Pat. No. 3,948,098 issued to Richardson, where a plate is placed in a flowing fluid and a piezo-electric element senses changes in pressure caused by the vortices shed from the plate. The piezo-electric element generates an alternating voltage at a frequency that corresponds to the vortex pressure pulses and the flow rate of the fluid.
Although these and other devices have been developed that measure fluid flow based on the measurement of vortices or the oscillation of an object in a fluid flow, such fluid flow measurement technique has not seen widespread application. Those of ordinary skill in the sewage flow measurement art have instead focused on other technologies when developing sewage flow measurement devices. As a result, there is a need for improvement in the field of sewage flow measurement.
Specifically, many conventional sewage flow meters and associated techniques are often beyond the financial capacity and skill set of small and medium sized sanitary system authorities. Also, because of the cost and complexity of these evaluation methods, a complete review of the entire sanitary system is typically not performed by sanitary system authorities capable of affording such techniques and software. Thus, although general problem areas in the system may be identified, specific pipe restrictions and blockages may be missed.
Due to the cost of employing data collection personnel and consultants, the review and analysis of most sanitary sewer systems is typically short lived, and usually only performed in response to a specific problem or overflow. Prior art evaluation techniques are typically project-based, specific to a particular problem and not designed for ongoing assessment of the collection network. The resultant data is typically not incorporated into the ongoing operation and maintenance procedures of the authority, and is therefore not helpful in identifying and solving future problems in the system.
Moreover, flow measurement studies are merely the first step in addressing an infiltration and inflow problem. After the study has been conducted, the potential problem areas identified must be further evaluated and inspected to determine if infiltration is actually occurring, how it is occurring and how it may be addressed. This inspection may require actual physical examination of the piping by personnel and/or inspection of the piping with cameras and closed circuit television (CCTV). This critical next step can be expensive and difficult to conduct.
The value of any flow measurement study depends on its ability to accurately predict the precise portion of the system where infiltration and inflow may be occurring. If the study merely identifies large portions of the system that have infiltration, the study is essentially useless because these large portions must still be inspected.
Those of skill in the art have developed complex methodologies and expensive solutions to provide greater precision in identifying the potential location of infiltration and inflow. Some advocate increasing the flow detection points during a wet weather study to more accurately identify the portions of the system experiencing infiltration and inflow. Although this solution may be cost effective because it decreases the cost of the next step in the process, this solution is nonetheless very expensive and beyond the financial capabilities of many small and medium sized sanitary sewer system authorities. Sewage flow measurement devices are expensive, and the additional personnel required to monitor and measure additional points in the system also increases the expense of the sewage flow measurement study.
Others have developed complex sewer system modeling techniques and software for evaluating the performance of a system and predicting the effect of inflow and infiltration during a wet weather event. These techniques often require extended on-sight evaluations by consultants, which further increases the cost. Thus, there is a need for accurately and economically pinpointing the source of infiltration and inflow into a sanitary sewer system, whereby managers and owners of such systems may conduct sewage flow measurement studies that accurately predict where infiltration and inflow are occurring.
Because the evaluation of sanitary sewer systems has historically been project-based and in response to a specific problem or overflow, little attention has been paid to the ongoing maintenance and upkeep of the system. However, sewer system assets that are not regularly maintained deteriorate faster, leading to higher replacement and emergency response costs. When a sewer system is regularly maintained, its lifetime can be increased and maintenance costs distributed over the lifetime of the system. Thus, a regular evaluation and maintenance program will save money in the long run, avoid unexpected and unplanned costs, and safeguard against the health risks associated with SSO's.
Accordingly, an object of the present invention is to provide an evaluation device and method for identifying potential causes of sanitary system overflows including restrictions and blockages in the piping system, ruptured or deteriorated pipes and sources of storm water inflow and infiltration into the system.
Another object of the present invention is to provide a method and device for measuring fluid flow in a sewage system based on the oscillations, tilt, and pressure exerted upon of an object in the sewage fluid flow.
A further object of the present invention is to provide an evaluation device and method that specifically identify problem points in the sewage collection network and avoid the need to build additional or redundant capacity in the sewage system.
Yet another object of the present invention is to provide a flow measurement device and that is inexpensive to administer, simple to use, does not significantly obstruct fluid flow, and is easily inserted into the fluid flow to obtain a measurement.
Another object of the present invention is to provide an evaluation method that can be incorporated as part of an ongoing sewer system maintenance and upkeep program to prolong the life of the system and avoid unexpected costs.
Another object of the present invention is to provide an evaluation method that reduces the cost of conducting an infiltration and inflow study by minimizing the time that consultants and engineers must be on-sight to evaluate the system.
A still further object of the present invention is to provide an evaluation method that utilizes available data and technology not previously available for the analysis of sanitary sewer systems.
Finally, another object of the present invention is to provide evaluation methods that more efficiently predict the location of infiltration and inflow when compared to conventional sewage flow analysis methods.